| 摘要 |
PROBLEM TO BE SOLVED: To prevent the chances of causing a cross talk by providing the variable diaphragm in which the first and the second light beams, that are made incident from an optical path changing means, are totally passed or partially passed to an objective lens and forming the light spots having only main lobes on the respective information recording surfaces of different disks by the lens. SOLUTION: First and second light beams from first and second light sources 305 and 375 having wavelengths of 635 nm and 780 nm, respectively are transmitted to an objective lens 7 through first and second hologram type optical dividers 32 and 36, a first optical divider 33, a first collimation lens 34 and a hologram type variable diaphragm 35. The diaphragm 35 has a first region, whose numerical aperture is less than 0.36 and a second region, whose numerical aperture is more than 0.36. The first region totally passes the first and the second light beams. The second region totally passes the first light beams and partially passes the second light beams. Thus, the lens 7 forms the light spots which have only main lobes on the recording surface of a DVD 8 and a CD-R 9 and the cross talk generated by side-lobes is prevented. |
